1. Field of the Invention
The present disclosure relates generally to electric fluid pumps of the type used in motor vehicles, and more particularly to an electric fluid pump having a rotor unit with a magnet carrier assembly including a pair of coaxial components fixed together and a method of constructing the rotor unit.
2. Related Art
This section provides background information related to the present disclosure which is not necessarily prior art.
As is well known, a water pump circulates a liquid coolant through a vehicle's coolant system to transfer heat from the engine for optimized engine performance as well as for use in heating the passenger cabin. Water pumps are largely divided into two classifications including mechanical water pumps and electric water pumps. Mechanical water pumps are typically driven by the engine via an accessory drive system (i.e. pulley and belt system). As such, the flow rate characteristics of mechanical water pumps are primarily dependent on the engine speed. To provide variable control of the flow rate independent of the engine speed, the coolant system is equipped with an electric water pump. The electric water pump typically includes an impeller driven by a variable-speed electric motor controlled by a control apparatus or system. As the number of vehicles equipped with an electric water pump continues to increase, a need exists to develop electrically-operated pump components that can provide enhanced performance and durability.
In many conventional electric water pumps, the rotor unit includes a “molded” magnet carrier within which a plurality of magnets are completely encapsulated. One example of an over-molded magnetic carrier in a rotor of an electric water pump is disclosed in U.S. Pat. No. 8,747,082. However, the process of over-molding the magnets within the plastic carrier is complicated by various characteristic including, without limitation, magnet tolerances, excessive flash, poor mold fill, inadequate magnet retention and imbalance issues. Accordingly, a recognized need exists to identify and develop alternative magnet retention systems for rotor units in electric water pumps.